You ARE the alien
I think a lot of people fail to realize something "obvious" about themselves.
We are living, thinking creatures. We exist in reality in this universe.
We, humans, and all life forms on Earth collectively, we are the aliens.
Perhaps it is the case that life as we know it developed on Earth independently? We don't know.
But even if Earthly creatures are Generation 0 of an intergalactic alien civilization, that's still an alien. Just an early one! It very well could be the case that DNA made an intergalactic journey to reach Earth in the first place.
DNA, not humans, represent the unit economics of alien life. Humans are important for producing cognition capable of observing the universe from within, of course, but a human cannot space travel. DNA is the underlying construct that knows how to perform labor and reproduce.
The most important task for humanity is to spread DNA across the cosmos. If we are the only aliens to exist, it's our responsibility.